1. Field of the Invention
This invention relates to a method of actuating optical fibers for optical scanning devices used for optical scanning endoscopes, optical scanning microscopes, optical scanning projectors, or the like in which an optical fiber vibration scanning is used.
2. Description of Related Art
Endoscopes in which scanning is performed by an optical fiber includes an endoscope disclosed in Japanese Patent TOKUHYOU No. 2010-527028. In the endoscope disclosed in Japanese Patent TOKUHYOU No. 2010-527028, piezoelectric devices B are put on the base of an optical fiber A in two directions as shown in FIG. 5 and produce resonant vibration in the X- and Y-directions, so that a beam of light is scanned. And, resonant vibration is used for scanning in the endoscope disclosed in Japanese Patent TOKUHYOU No. 2010-527028, so that drive frequencies in the X- and Y-directions become approximately equal to each other and its scan pattern becomes spiral as shown in FIG. 7. Also, in this scanning for which resonant vibration is used, modulation is performed by increasing or decreasing amplitude gradually, so that driving signals are complicated. Also, the center of the spiral scan pattern is widely different from the periphery of the spiral scan pattern in scanning speed.
On the other hand, it is possible to scan a beam of light with a raster pattern as shown in FIG. 8 by making drive frequencies in the X- and Y-directions widely differ from each other to synchronize the drive frequencies in the X- and Y-directions. This scanning does not require amplitude modulation, drive signals become simple, and it is possible scan a beam of light on a rectangular region, so that an image conversion can be performed without waste. Also, the scanning pitch in the vicinity of the center of the scan pattern is uniform, the vicinity of the center of the scan pattern becoming an object to be observed mainly. As a result, exposure time for an object to be imaged is uniform.
Also, endoscopes in which a scanning by an optical fiber is performed using electromagnetic drive include an endoscope disclosed in Japanese Patent TOKUKAI No. 2008-116922. In the endoscopes disclosed in Japanese Patent TOKUKAI No. 2008-116922, magnets C1 and C2 are fitted to an optical fiber A as shown in FIG. 6, electromagnetic coils D are arranged around the magnets C1 and C2, and the optical fiber A is driven using electromagnetic force. And, a non-resonant scanning by the optical fiber A is performed at low speed in the Y-direction and a scanning by the optical fiber A is performed at a second-order resonant frequency in the X-direction so that the scanning is performed with a raster pattern that is shown in FIG. 8.